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<span id="Extended-I_002fO-specifiers"></span><div class="header">
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<hr>
<span id="Extended-I_002fO-specifiers-1"></span><h4 class="subsection">5.1.32 Extended I/O specifiers</h4>
<span id="index-CARRIAGECONTROL"></span>
<span id="index-READONLY"></span>
<span id="index-SHARE"></span>
<span id="index-SHARED"></span>
<span id="index-NOSHARED"></span>
<span id="index-I_002fO-specifiers"></span>

<p>GNU Fortran supports the additional legacy I/O specifiers
<code>CARRIAGECONTROL</code>, <code>READONLY</code>, and <code>SHARE</code> with the
compile flag <samp>-fdec</samp>, for compatibility.
</p>
<dl compact="compact">
<dt><code>CARRIAGECONTROL</code></dt>
<dd><p>The <code>CARRIAGECONTROL</code> specifier allows a user to control line
termination settings between output records for an I/O unit. The specifier has
no meaning for readonly files. When <code>CARRAIGECONTROL</code> is specified upon
opening a unit for formatted writing, the exact <code>CARRIAGECONTROL</code> setting
determines what characters to write between output records. The syntax is:
</p>
<div class="example">
<pre class="example">OPEN(..., CARRIAGECONTROL=cc)
</pre></div>

<p>Where <em>cc</em> is a character expression that evaluates to one of the
following values:
</p>
<table>
<tr><td width="20%"><code>'LIST'</code></td><td width="80%">One line feed between records (default)</td></tr>
<tr><td width="20%"><code>'FORTRAN'</code></td><td width="80%">Legacy interpretation of the first character (see below)</td></tr>
<tr><td width="20%"><code>'NONE'</code></td><td width="80%">No separator between records</td></tr>
</table>

<p>With <code>CARRIAGECONTROL='FORTRAN'</code>, when a record is written, the first
character of the input record is not written, and instead determines the output
record separator as follows:
</p>
<table>
<thead><tr><th width="30%">Leading character</th><th width="30%">Meaning</th><th width="40%">Output separating character(s)</th></tr></thead>
<tr><td width="30%"><code>'+'</code></td><td width="30%">Overprinting</td><td width="40%">Carriage return only</td></tr>
<tr><td width="30%"><code>'-'</code></td><td width="30%">New line</td><td width="40%">Line feed and carriage return</td></tr>
<tr><td width="30%"><code>'0'</code></td><td width="30%">Skip line</td><td width="40%">Two line feeds and carriage return</td></tr>
<tr><td width="30%"><code>'1'</code></td><td width="30%">New page</td><td width="40%">Form feed and carriage return</td></tr>
<tr><td width="30%"><code>'$'</code></td><td width="30%">Prompting</td><td width="40%">Line feed (no carriage return)</td></tr>
<tr><td width="30%"><code>CHAR(0)</code></td><td width="30%">Overprinting (no advance)</td><td width="40%">None</td></tr>
</table>

</dd>
<dt><code>READONLY</code></dt>
<dd><p>The <code>READONLY</code> specifier may be given upon opening a unit, and is
equivalent to specifying <code>ACTION='READ'</code>, except that the file may not be
deleted on close (i.e. <code>CLOSE</code> with <code>STATUS=&quot;DELETE&quot;</code>). The syntax
is:
</p>
<div class="example">
<pre class="example"><code>OPEN(..., READONLY)</code>
</pre></div>

</dd>
<dt><code>SHARE</code></dt>
<dd><p>The <code>SHARE</code> specifier allows system-level locking on a unit upon opening
it for controlled access from multiple processes/threads. The <code>SHARE</code>
specifier has several forms:
</p>
<div class="example">
<pre class="example">OPEN(..., SHARE=sh)
OPEN(..., SHARED)
OPEN(..., NOSHARED)
</pre></div>

<p>Where <em>sh</em> in the first form is a character expression that evaluates to
a value as seen in the table below. The latter two forms are aliases
for particular values of <em>sh</em>:
</p>
<table>
<thead><tr><th width="30%">Explicit form</th><th width="30%">Short form</th><th width="40%">Meaning</th></tr></thead>
<tr><td width="30%"><code>SHARE='DENYRW'</code></td><td width="30%"><code>NOSHARED</code></td><td width="40%">Exclusive (write) lock</td></tr>
<tr><td width="30%"><code>SHARE='DENYNONE'</code></td><td width="30%"><code>SHARED</code></td><td width="40%">Shared (read) lock</td></tr>
</table>

<p>In general only one process may hold an exclusive (write) lock for a given file
at a time, whereas many processes may hold shared (read) locks for the same
file.
</p>
<p>The behavior of locking may vary with your operating system. On POSIX systems,
locking is implemented with <code>fcntl</code>. Consult your corresponding operating
system&rsquo;s manual pages for further details. Locking via <code>SHARE=</code> is not
supported on other systems.
</p>
</dd>
</dl>

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